Portable Magnet Impedance Meter Based On Four-line Method

In daily scientific research,it is often necessary to measure the resistance and inductance with smaller values,such as device contact resistance,wire resistance,winding resistance of transformers,motors,magnets,circuit board wire impedance,etc.These impedance values have design and accuracy for circuits and devices.Influence,and in the operation of the device,the change of the impedance value has important reference and research significance for the structure,operating state,temperature change,and cause of equipment failure.But in practical work,because these impedance values are too weak,the impedance of this level can not be accurately measured by the commonly used multimeter,and the error is too large.Therefore,a special device for measuring weak impedance is needed to realize the accurate measurement and monitoring of the impedance parameters of magnets and components.In this paper,the four-wire measurement method of separating voltage port and current port is used to effectively avoid the influence of lead resistance of probe and contact resistance produced by Kelvin clip on measurement accuracy.At the same time,the traditional measurement mode of Kelvin bridge with standard resistance is abandoned,and the hardware design is optimized by using full digital measurement method,which makes the instrument miniaturized and portable.The constant current source with PI feedback amplification and high precision analog-to-digital converter are used for sampling in the design of the instrument.The constant current generated by the constant current source is controlled by the internal program of the microprocessor.According to the different characteristics of impedance,the DC and AC separated modes are used to measure the constant current.The DC mode generates the numerically controllable DC current,and the AC mode generates the AC mode with controllable amplitude and frequency.Current current is used to measure DC resistance and AC inductance respectively.Current acts on the impedance to be measured and generates voltage.High-precision analog-to-digital converter is used to measure the voltage parameters of impedance to be measured.After the corresponding calculation of digital algorithm in microprocessor,the current is displayed on LCD display screen,and the impedance can be measured accurately and intuitively through wireless serial port.Through the hardware and software design of the instrument,the assembly of the instrument and the code compilation and debugging of each functional module are completed.After the debugging is completed and the module function is successfully realized,the impedance measurement experiment is carried out.The precision sampling resistance measurement experiment,magnet resistance measurement experiment,ring inductor measurement experiment and magnet inductance measurement experiment were carried out.The measurement environment was selected to test the temperature drift performance of the instrument.The IM3536 high precision LCR meter produced by HIOKI Company was selected to compare the experimental data.After the analysis of the experimental data,the measuring accuracy of the instrument was basically acceptable.To achieve 0.1%~0.5%,and has good temperature stability,basically in line with the design requirements.